1. Field of the Invention
This invention relates to the mining of coal, and more particularly, to methods of obstructing or blocking the deleterious flow of methane gas into the mine from the coal seam.
2. Brief Description of the Prior Art
U.S. Pat. No 3,845,632 to Slobod and Burcik describes a method for obstructing or blocking the flow of methane gas from a coal seam into a mine entry formed in the seam by drilling holes into the seam, and injecting a gelable silicic acid composition via these holes into the cracks and fissures which exist naturally in the coal at the cleavage planes thereof. The silicic acid gel which results after such injection forms a blockage in the cracks and fissures existing at the cleavage planes of the coal, and prevents traverse of these cracks and fissures by methane gas so as to enter the mine at a location where these cracks intersect a mine face.
In carrying out the process of attaining blockage of gas flow using a silicic acid gel, the silicic acid composition, when initially infused through the bore holes formed in the seam, must be of low viscosity and quite fluid, so that gelling does not occur prior to the dispersion of the silicic acid into the natural cracks and fissures intersected by the bore holes. Care must also be exercised to make certain that lumps or solid particles do not form in the pre-mixed silicic acid composition which will block free flow into the cracks and fissures, or which will be filtered out by very small cracks located along the hole. It is also necessary, in using the silicic acid method of blocking, to very closely control the time interval over which the composition can set up or gel to a semi-solid state so that it completely fills the cracks and fissures without slumping due to late setting, and so that it does not gel prematurely, thus requiring excessively high pressures or completely arresting the infusion.
In the technology of oil and gas production, it is known to fracture certain subterranean formations to enhance or increase production therefrom by providing a directionally oriented notch in the formation to be fractured, followed by the injection into the notch of a relatively viscous fluid under high pressure so that the natural forces of adhesion in the rock, along with the natural rock stresses, are overcome, and a fracture is propagated from the notch for a substantial distance into the formation. A technique of this general type is disclosed in U.S. Pat. No. 3,106,959.